iOS build: Replace %20 with space in config script

CLA: trivial

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9297)

(cherry picked from commit 53fd220c8fc953b603dd13257d6b2e2d1e7eb864)